CN115503301A - A kind of natural fiber reinforced thermoplastic composite material and preparation method thereof - Google Patents

Abstract

The invention relates to a natural fiber reinforced thermoplastic composite material and a preparation method thereof, wherein the composite material is of a sandwich structure, the surface layer is natural fiber directional woven fiber cloth, and the middle layer is a random directional long natural fiber and thermoplastic resin blended composite layer; and an interface layer formed by inserting the random oriented long natural fibers into the pores of the oriented woven fiber cloth is arranged between the surface layer and the middle layer. The invention has high interlayer strength, improves the integral bending strength and impact strength of the material, can completely reserve the surface woven texture, realizes the spraying-free surface texture and has good comprehensive performance.

Description

A kind of natural fiber reinforced thermoplastic composite material and preparation method thereof

technical field

The invention belongs to the field of composite materials, in particular to a natural fiber reinforced thermoplastic composite material and a preparation method thereof.

Background technique

The fiber-reinforced composite material with thermosetting resin as the matrix generally requires a long molding time, for example, the fiber-reinforced composite material is obtained by heating and pressing the prepreg in an autoclave for more than 2 hours. Composite materials that use thermoplastic resins instead of conventional thermosetting resins as the matrix can significantly shorten the molding time and are recyclable, which has attracted a lot of attention in development and research.

As a green, environmentally friendly and low-cost raw material, natural fibers can replace glass fibers or carbon fibers as reinforcements for composite materials. There have been many studies on natural fiber reinforced thermoplastic composites. Among them, continuous natural fiber cloth and thermoplastic resin are generally laminated, or disordered fibers are combined with thermoplastic resin. If the continuous natural fiber cloth is used as the surface layer and the disordered fiber is used as the core layer, composite materials with surface patterns can be obtained, but often the interface between three or more layers is only connected by resin, which becomes the weak point of the overall material.

Contents of the invention

The technical problem to be solved by the present invention is to provide a natural fiber reinforced thermoplastic composite material and a preparation method thereof. Spray surface texture, with good comprehensive performance.

The invention provides a natural fiber-reinforced thermoplastic composite material, the composite material is a sandwich structure, the upper and lower surface layers are directional woven fiber cloth of natural fibers, and the middle layer is a blended composite layer of randomly oriented long natural fibers and thermoplastic resin; the surface layer Between the interlayer and the middle layer is the interface layer formed by randomly oriented long natural fibers inserted into the pores of oriented woven fiber cloth (natural fiber is woven fiber cloth, generally unidirectional tape or plain weave, twill cloth, etc.; random oriented long natural fiber is cut Monofilaments of natural fibers, randomly sprayed, so the fiber direction is randomly oriented).

The natural fiber is one or more of hemp fiber, cotton fiber, bamboo fiber, ramie fiber, flax fiber, jute fiber and silk fiber.

The natural fiber directional weaving fiber cloth is a two-dimensional or three-dimensional weaving fiber cloth, such as unidirectional fiber and bidirectional weaving fiber such as yarn, rabbet, etc.; the porosity is 10-50%, and the hole area ranges from 0.01-1mm ² .

The thermoplastic resin is one or more of polyamide, polypropylene, polyethylene, polymethyl methacrylate, polycarbonate, polybutylene terephthalate; the thermoplastic resin is fibrous, granular or liquid. Modified polypropylene PP is preferred.

The blending volume ratio of the randomly oriented long natural fibers to the thermoplastic resin is 30-60:40-70; the length of the randomly oriented long natural fibers is 10-100 mm.

The thickness ratio of the surface layer to the middle layer is 1:3-1:10; the thickness of the interface layer accounts for 2.5-50% of the total thickness.

The present invention also provides a method for preparing a natural fiber reinforced thermoplastic composite material, comprising:

(1) cutting long natural fibers, loosening the randomly oriented long natural fibers obtained by cutting, spreading them with thermoplastic resin on the directional woven fiber cloth of natural fibers, and fixing them under pressure to obtain a multi-layer mixed fiber mat;

(2) Raise the temperature of the multi-layer mixed fiber mat and pressurize it until the resin is melted, so that the thermoplastic resin is impregnated in the space between the directional woven fiber cloth and the long natural fiber, then cooled, and put into the mold; the temperature of the mold is raised To the softening point or above the melting point of the thermoplastic resin, the mold is molded and then cooled to obtain a natural fiber-reinforced thermoplastic composite material.

The pressurized and fixed process parameters in the step (1) are: temperature 80° C.-100° C., pressure 4-5 MPa, keep the pressure for 0.5-2 minutes, and exhaust and remove moisture at the same time.

The process parameters of stage heating and stage pressurization in the step (2) are: 10° C./min heats up to 150° C., pressurizes to 5 MPa, and then releases the pressure to 1 MPa for exhausting; then heats up to 180-195° C. ( Depending on the melting point or softening point of the thermoplastic resin), pressurize at 10-12MPa, hold the pressure for 10min, and then cool to open the mold.

Beneficial effect

The present invention has high interlayer strength, the overall bending strength and impact strength of the material have been improved, the weaving texture of the surface layer can be completely preserved, and the spray-free surface texture is realized, which has good comprehensive performance; the raw materials used are 100% recyclable materials, and recycled broken materials It can be mixed with long natural fibers in proportion to make the middle layer structure, and the addition ratio is 20-50%, which will not affect the performance of the final product; the directional woven fiber cloth can be produced continuously and has the characteristics of high-efficiency production.

Description of drawings

Fig. 1 is the structural representation of natural fiber reinforced thermoplastic composite material of the present invention;

Fig. 2 is a schematic diagram of the preparation process of the natural fiber reinforced thermoplastic composite material of the present invention.

detailed description

Below in conjunction with specific embodiment, further illustrate the present invention. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the teachings of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of the present application.

Porosity refers to the ratio of the pore area contained in the oriented fiber cloth to the total area, expressed in percentage (%). The interface layer thickness h can be observed by SEM. Interface layer thickness ratio=2h/(A+B+A)*100%. A is the thickness of the surface layer of natural fiber oriented woven fiber cloth, and B is the thickness of the middle layer of randomly oriented long natural fiber and thermoplastic resin blended composite layer.

The preparation method of embodiment and comparative example comprises the following steps

(1) Cutting natural fibers, loosening the randomly oriented long natural fibers obtained by cutting, spreading them with thermoplastic resin on the directional weaving fiber cloth of natural fibers, and fixing them under pressure to obtain a multi-layer mixed fiber mat;

(2) The thermoplastic resin in the multi-layer mixed fiber mat is heated up step by step under pressure, and the step is pressurized until the resin is melted, so that the thermoplastic resin is impregnated in the space between the directional woven fiber cloth and the long natural fiber, and then cooled, put into In the mold; the temperature of the mold is raised to above the softening point or melting point of the thermoplastic resin, the mold is closed and shaped and then cooled to obtain a natural fiber-reinforced thermoplastic composite material.

The pressurized and fixed process parameters in the step (1) are: temperature 80° C.-100° C., pressure 4-5 MPa, keep the pressure for 0.5-2 minutes, and exhaust and remove moisture at the same time.

The process parameters of stage heating and stage pressurization in the step (2) are: 10° C./min heats up to 150° C., pressurizes to 5 MPa, and then releases the pressure to 1 MPa for exhausting; then heats up to 180-195° C. ( Depending on the melting point or softening point of the thermoplastic resin), pressurize at 10-12MPa, hold the pressure for 10min, and then cool to open the mold.

It can be seen in Comparative Example 1 that the randomly oriented long natural fibers alone have low strength and good toughness, and at the same time the surface effect is poor, and subsequent painting is required; in Comparative Example 2, it can be seen that the fiber cloth is combined with PP, which has high strength and poor toughness; in Comparative Example 3, pores can be seen Ratio is too high, strength and toughness decline; Comparative example 4 shows that the natural fiber content of B layer is too high, causes infiltration deficiency, strength and toughness decline; Embodiment 1 shows that suitable porosity and B layer composition and interlayer thickness, can Reach better strengthening and toughening effect; It can be seen from Example 2 that adding 30% recycled materials has little change in strength and toughness; It can be seen from Example 3 that the thickness of the fiber cloth is reduced, the strength is slightly reduced, and the impact is slightly increased; Example 4 As can be seen from Comparative Example 5, the effect of increasing strength and toughness can also be achieved with liquid MMA.

Claims (9)

1. A natural fiber reinforced thermoplastic composite material is characterized in that: the composite material is a sandwich structure, the surface layer is a natural fiber directional weaving fiber cloth, and the middle layer is a blended composite layer of randomly oriented long natural fiber and thermoplastic resin; Between the surface layer and the middle layer is an interface layer formed by randomly oriented long natural fibers inserted into the pores of the oriented woven fiber cloth. 2. The composite material according to claim 1, characterized in that: the natural fiber is one or more of hemp fiber, cotton fiber, bamboo fiber, ramie fiber, flax fiber, jute fiber and silk fiber. 3. The composite material according to claim 1, characterized in that: the directional woven fiber cloth of natural fibers is a two-dimensional or three-dimensional woven fiber cloth with a porosity of 10-50% and a pore area of 0.01-1 mm ² . 4. The composite material according to claim 1, characterized in that: said thermoplastic resin is polyamide, polypropylene, polyethylene, polymethyl methacrylate, polycarbonate, polybutylene terephthalate One or more of them; the thermoplastic resin is fibrous, granular or liquid. 5. The composite material according to claim 1, characterized in that: the volume content of the randomly oriented long natural fibers is 20%-50%, and the volume content of the thermoplastic resin is 50%-80%; the length of the randomly oriented long natural fibers 10-100mm. 6. The composite material according to claim 1, characterized in that: the thickness ratio of the surface layer to the middle layer is 1:3-1:10; the thickness of the interface layer accounts for 2.5-50% of the total thickness. 7. A method for preparing a natural fiber reinforced thermoplastic composite material, comprising: (1) cutting long natural fibers, loosening the randomly oriented long natural fibers obtained by cutting, spreading them with thermoplastic resin on the directional woven fiber cloth of natural fibers, and fixing them under pressure to obtain a multi-layer mixed fiber mat; (2) The multi-layer mixed fiber is heated up in stages and pressurized in stages until the resin is melted, so that the thermoplastic resin is impregnated in the space between the directional woven fiber cloth and the long natural fiber, then cooled, and put into the mold; the temperature of the mold is raised to The thermoplastic resin is above the softening point or melting point, and then cooled after the mold is closed to obtain a natural fiber-reinforced thermoplastic composite material. 8. The preparation method according to claim 7, characterized in that: the pressurized and fixed process parameters in the step (1) are: temperature 80°C-100°C, pressure 4-5MPa, maintaining pressure 0.5-2min, while Exhaust and remove moisture. 9. The preparation method according to claim 7, characterized in that: the process parameters of the staged heating and staged pressurization in the step (2) are: 10°C/min to heat up to 150°C, pressurize to 5MPa, and then release the pressure to 1MPa; then raise the temperature to 180-195°C, pressurize at 10-12MPa, keep the pressure for 10min, and then cool and open the mold.

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